The present invention is directed to a system and method for detecting the fill point of a fluid clutch. More particularly, the present invention is directed to a system and method for detecting the fill point of a fluid clutch based on the pressure of a fluid supply line.
Most vehicles include a transmission that translates the rotational speed of an engine shaft into a drive speed for the vehicle. A transmission typically includes a series of gears that may be selectively engaged to provide a series of gear ratios that translate the speed of the engine shaft into different drive speeds. The gear ratios usually include forward and reverse gears that range from low to high to provide different powers and speeds for the vehicle as different operating conditions are encountered. A desired gear ratio may be obtained by engaging one or more clutches within the transmission. The engagement of a clutch may connect a pair of gears to thereby transmit the torque of the engine shaft. The difference between the rotational speed of the engine shaft and the drive speed depends upon the gear ratio of the connected gears.
A transmission may utilize many types of clutches such as, for example, fluid clutches or mechanical clutches to engage a particular gear ratio. Each type of clutch may connect a moving part to a non-moving part through a frictional engagement. A force may need to be applied to one of the moving or the non-moving parts to effect the frictional engagement. In a mechanical clutch, this force may be generated by a spring. In a fluid clutch, this force may be generated by fluid pressure.
When, for example, a force is applied to a non-moving part to engage a clutch, the non-moving part will gradually engage the moving part as the force of the clutch is increased. If the force is applied too rapidly, the vehicle will jump or jerk when the clutch engages. If the force is not great enough to completely engage the parts, the clutch may slip, causing the vehicle to shake.
In a fluid clutch, a pressurized fluid may be introduced into a chamber to create the engagement force. A control valve typically governs the flow of fluid into the clutch. To engage the clutch, the control valve is opened to allow a restricted flow of fluid to enter and fill the clutch chamber. Once the chamber is filled with fluid, the valve is gradually modulated to a maximum open position to gradually increase the pressure of the fluid and the engagement force of the clutch. If the valve is modulated open too quickly, or modulated open prior to the clutch chamber filling with fluid, the clutch engagement may occur too quickly and cause the vehicle to jump or jerk.
A transmission will typically include a system or method for determining the time required to fill the clutch chamber. As described in U.S. Pat. No. 5,737,979, the fill time for a particular clutch may be determined by a calibration process. In the calibration process, the fill time for a particular clutch is carefully measured under a variety of operating conditions, such as, for example, different engine speeds and fluid temperatures. The fill times are stored as xe2x80x9clook up tablesxe2x80x9d in the memory of a control unit. During standard operation, the control unit accesses these xe2x80x9clook up tablesxe2x80x9d to determine the appropriate fill time for a clutch based on the current operating conditions. After the allotted fill time has expired, the control will gradually modulate the valve to the fully open position to increase the pressure of the fluid in the clutch chamber and complete the clutch engagement.
The calibration process required to determine the clutch fill time on a transmission may be expensive and inconvenient. Typically, a skilled technician and special equipment are required to perform the calibration. However, this may require that a transmission be sent to an off-site maintenance facility.
The fluid clutch fill detection system and method of the present invention solves one or more of the problems set forth above.
One aspect of the present invention is directed to a method of controlling a transmission. A command is received to engage a clutch having a chamber. A control valve is opened to allow pressurized fluid to flow from a fluid supply line into the clutch chamber. The pressure of the fluid within the fluid supply line is monitored as fluid flows through the control valve to enter the clutch chamber. A rate of change in the volume of fluid entering the clutch chamber is determined based on the sensed pressure of the fluid within the fluid supply line. A fill point of the clutch chamber is detected when the rate of change in the volume of fluid entering the clutch chamber is less than a volume differential threshold.
In another aspect, the present invention is directed to a control system for a transmission. The transmission includes a source of pressurized fluid, at least one clutch having a chamber, at least one control valve, and a fluid supply line connecting the source of pressurized fluid with the at least one control valve. The control system includes a pressure sensor disposed in the fluid supply line between the source of pressurized fluid and the at least one control valve to sense the pressure of the fluid in the fluid supply line. A control is configured to selectively open the at least one control valve to allow pressurized fluid to enter the chamber of the at least one clutch, to monitor the pressure of the fluid in the fluid supply line, and to determine when the chamber of the at least one clutch is filled with fluid based on the monitored pressure of the fluid in the fluid supply line.